1. Field of the Invention
This invention relates generally to data disk drive systems and more particularly to servo systems for keeping the transducer head on track.
2. Description of the Prior Art
In electronic computer technology, it is common to store data in binary form on the face of a rotatable disk. The face of the disk is coated with a magnetizable substance such as iron oxide. The disks are operated by rotating them like phonograph records and the binary data is encoded upon, or retrieved from, the face of the disk by a movable magnetic transducer device called a read/write or transducer head. The binary information is encoded on the face of the disk in concentric rings, called tracks, and the read/write head can move radially along the disk face to select a particular track to record or retrieve information. The data disks can be rigid or flexible.
The removable rigid disks typically have track densities of about five hundred tracks per inch of radius of the disk. The flexible disks typically have densities of forty-eight or ninety-six tracks per inch. Because of the high density, precise positioning of the read/write head is necessary so that the head can accurately gain access to a particular desired track on the surface of the disk and follow the track as the disk rotates.
In order to obtain precise positioning when seeking a desired track, the disk drives sometimes have a glass scale which provides the disk drive with coarse information on the position of the read/write head. Once the head reaches a desired track, a method is needed to keep the head on track as the disk rotates. One such method for flexible disks involves the use of servo sectors and is disclosed by a co-pending application for "Servo Synchronization Method and Apparatus for a Magnetic Disk", Ser. No. 06/918,502, filed on Oct. 14, 1986, by the same inventor which is assigned to the same assignee as in the present application. The servo sector tracks contain positioning data to help the transducer heads stay on the data track. The servo tracks are radially off-set from the data tracks such that a transducer head passes between the servo tracks when it is positioned along a data track.
The consecutive servo tracks alternate between having an "A" burst and a "B" burst. The transducer head reads the "A" and "B" bursts from the servo tracks on either side. The intensities of the "A" and "B" bursts are measured and the head is adjusted to keep the head midway between the servo tracks and directly on the data track.
In order for the data disk to have the maximum data storage capacity, a number of servo sectors should be kept to a minimum. However, if there are not enough servo sectors per revolution, then the heads cannot stay on track.